Wireless sensors can be implanted within the body and used to monitor physical conditions, such as pressure or temperature. These sensors can be used to monitor physical conditions within the heart or an abdominal aneurysm. An abdominal aortic aneurysm (AAA) is a dilatation and weakening of the abdominal aorta that can lead to aortic rupture and sudden death. In the case of a repaired abdominal aneurysm, a sensor can be used to monitor pressure within the aneurysm sac to determine whether the intervention is leaking. The standard treatment for AAAs employs the use of stent-grafts that are implanted via endovascular techniques. However, a significant problem that has emerged with these stent-grafts for AAAs is acute and late leaks of blood into the aneurysm's sac. Currently, following stent-graft implantation, patients are subjected to periodic evaluation via abdominal CT (Computed Tomography) with IV contrast to identify the potential presence of stent-graft leaks. This is an expensive, risky procedure that lacks appropriate sensitivity to detect small leaks.
Typically, the sensors utilize an inductive-capacitive (“LC”) resonant circuit with a variable capacitor. The capacitance of the circuit varies with the pressure of the environment in which the sensor is located and thus, the resonant frequency of the circuit varies as the pressure varies. Thus, the resonant frequency of the circuit can be used to calculate pressure.
Ideally, the resonant frequency is determined using a non-invasive procedure. The signal from the sensor is weak relative to the signal used to energize the sensor, but is the same frequency and dissipates quickly. In one embodiment, the difference between the signals is on the order of 150 dB and the sensor signal is sampled approximately 35 nanoseconds after the energizing signal is turned off. In order to communicate with the sensor, the system uses a coupling loop and a cable assembly. For example, a person with an implanted sensor may lie, sit, or stand close to or in contact with a flexible antenna or coupling loop. Due to the unique characteristics of the transmitted and received signals the coupling loop and the cable assembly need to isolate the energizing signal and the sensor signal, support the necessary sampling speed, and support a relatively large bandwidth.
Some antennas or coupling loops use a capacitor soldered to the antenna to reduce mismatch losses. One problem with this approach is that the antenna may be flexed by the patient's weight and in some embodiments the solder joint may break or otherwise become inoperable. Accordingly, a need exists for a flexible antenna that meets the bandwidth requirement for communicating with a sensor implanted into a body that can withstand the patient's weight without breaking.
Some patients may need to have data retrieved from the implanted sensors relatively often. Conventional systems require the patient to come to the hospital to obtain and process data from the implanted sensor. Accordingly, a need exists for a data management system that can communicate implanted sensor data and/or processed data to a remote server and allow a physician or other individual to read and analyze the data.